/duy dim"ee euhm, di-/ , n. Chem.
a mixture of neodymium and praseodymium, formerly thought to be an element. Symbol: Di
[ dídym ( os ) twin (see DIDYMOUS) + -IUM; so named by Swedish chemist Carl Mosander (1797-1858), who discovered it in 1843, from its close association with lanthanum ]